Brown the ground beef, bacon and onions and drain grease if desired.
Add the ketchup, vinegar and brown sugar and simmer on low heat for 30 mins; stirring occasionally.
Drain you beans and toss in a 9x13 inch pan or 4 quart casserole dish.
Add the meat mixture on top of the beans and bake for 1.5 - 2 hours.
Notes
Different brands of pork and beans have more or less liquid. If your beans are on the dry side or you use the 9x13 in pan make sure to watch during cooking so they don't dry out.